“The Chameleon” fictionalizes an especially colorful chapter in the believe-it-or-not true story of Frédéric Bourdin, a French-born serial impostor and master of disguise who assumed scores of identities, especially those of missing teenagers. The movie focuses on one of his alter egos, Nicholas Barclay, a 13-year-old Texan from a working-class background who vanished without a trace in 1994 and “reappeared” three years later.

As if resurrected from the dead, a boy claiming to be Nicholas announced himself in Europe. An impostor who was actually 23, he traveled to the United States, where, despite his French accent and change of eye color, he convinced the family of his false identity. He claimed to have been kidnapped, taken to Europe, where he was tortured, raped and forced to work in a child prostitution ring. The ordeal left him so traumatized, he said, that his memories were blurred.

The movie — adapted from Christophe D’Antonio’s authorized biography of Mr. Bourdin, who is now living in western France and is married with children — changes the location of his American escapade from San Antonio to Baton Rouge, La., and Mr. Bourdin’s name to Frédéric Fortin. Fortin’s pseudonym in the film is Nicholas Mark Randall.

Marc-André Grondin, the 27-year-old Canadian actor who portrays Fortin, won acclaim playing a teenage misfit growing up in 1960s and ’70s Montreal in the Canadian film “C.R.A.Z.Y.” That brilliant, French-language movie never found a United States distributor despite being showered with Genie awards (the Canadian equivalent of the Oscars).

In “The Chameleon” Mr. Grondin works hard to fill out a character the screenplay doesn’t examine in enough depth to bring fully to life. But at least Mr. Grondin’s disturbingly creepy performance offers no pat explanations, and it doesn’t plead for our sympathy. His mysterious character is shown researching Nicholas’s identity on the Internet and shaving his body hair to appear younger. There are brief, scattered flashbacks to his French childhood.

Intriguing as it is, “The Chameleon” might have been a much stronger film had it been narrated by its central character and included a lot more of his personal history. His life, before and after his Texas adventure, seems ripe for a sprawling mini-series like “Carlos.” Or if not that, a picaresque serious comedy like “Catch Me if You Can.” In any case, “The Chameleon” feels too small for its subject.

From the beginning there is little question that Nicholas is an impostor. But why? The movie barely touches on that question except for its unsatisfying, sentimental conclusion that his con artistry was an appeal for love. If so, the emotional deprivation driving that search is not explored. We see the impostor’s trickery but not the pain driving it. Nicholas uses every manipulative ploy in the book to confound his supposed family and the law. Resisting interrogation, he throws tantrums, collapses in feigned fits of post-traumatic agony, and falls into long silences.

An error has occurred. Please try again later.

You are already subscribed to this email.

Another wrong decision of this film, the English-language directorial debut of Jean-Paul Salomé (“Arsène Lupin”) from a screenplay he wrote with Natalie Carter, is its framing of the story as a police procedural. It is told from perspective of Jennifer Johnson (Famke Janssen), the tough, fictional F.B.I. agent investigating Nicholas’s disappearance. Jennifer, well played by Ms. Janssen, badgers the impostor and his “family” for information as she tries to get to the bottom of what she suspects is the real Nicholas’s unsolved murder.

His relatives are a miserable lot. The most stable, his older sister Kathy (Emilie de Ravin), who works in a nail salon, embraces Nicholas with a ferocious protectiveness. His violent half brother Brendan (Nick Stahl), a sneering, hard-drinking bully with a cocaine problem, treats him with contempt while not actually contradicting his claims; he may know something about the real Nicholas’s disappearance that he is keeping to himself.

The mother, Kimberly (Ellen Barkin), a drunken, chain-smoking wreck who sometimes shoots heroin, shrinks from the fake Nicholas’s touch and can barely bring herself to look at him. “Just in case you haven’t forgotten, there wasn’t exactly sunshine between you and me,” she snarls. “You made my life hell.” Ms. Barkin is almost unrecognizable as this bedraggled bundle of rage and disappointment. Exploding from deep within, her devastating performance hijacks the film.

Directed by Jean-Paul Salomé; written by Mr. Salomé and Natalie Carter, based on the book by Christophe D’Antonio; director of photography, Pascal Ridao; edited by Marie-Pierre Renaud; music by Jeff Cardoni; production design by Martina Buckley; costumes by Susanna Puisto; produced by Cooper Richey, Bill Perkins, Ram Bergman, Marie-Castille Mention-Schaar and Pierre Kubel; released by LLeju Productions. At the Quad Cinema, 34 West 13th Street, Greenwich Village. Running time: 1 hour 33 minutes.